1. Technical Field
The present invention relates to a method of making a semiconductor package, and more especially, to a method of making multi-chip copper wire bonding semiconductor package.
2. Description of Related Art
A multi-chip semiconductor package usually requires a lead frame with more than one die pad to accommodate the multiple semiconductor chips. The die pads in a lead frame are mutually separated to maintain electrical isolation between different semiconductor chips, which is particular important for vertical semiconductor chips such as vertical metal oxide semiconductor field effect transistors (MOSFETs) where the drain electrode disposed on the bottom of MOSFET chip is electrically connected to the die pad. The mutually separated die pads are connected to the lead frame with tie bars in a few locations that may not provide adequate support in the wire bonding process, especially with the current trend to replace gold (Au) wires with copper (Cu) wires for cost reduction purposes. Cu wires are much harder and stronger than Au wires and therefore require much stronger force in the wire bonding process. For that reason the integrity of lead frame much improve to sustain the impact of Cu bond wire to achieve high quality electrical connections. On the other hand the leads layout of a certain package must remain the same for the new cost saving device to be adopted onto the same circuit board without costly design modification. An improved lead frame and assembly process are needed to achieve these goals.